Investigation of Flame Generated Turbulence in a Large-Scale and Low-Intensity Turbulent Premixed Flame with a 3-Element Electrostatic Probe and a 2-D LDV

Abstract

An attempt has been made to examine the flame-generated turbulence in a large-scale and low-intensity turbulent premixed flame by measuring change of the local gas-velocity vector across the flame front in relation with local movement of the flame front. In order to achieve this measurements, specially arranged diagnostics, composed of an electrostatic probe with three identical sensors and a two-color four beam LDV (laser-doppler velocimeter) system, have been adopted. From simultaneous measurements by these two instruments at the same point, local movement of the flame front in a vertical plane above a vertically oriented burner can be measured by the electrostatic probe, and simultaneously, the instantaneous axial and radial components of the local gas velocity in the same plane can be measured by the suitably oriented LDV system. Thus, change of the power spectrum density function and individual change of the local gas-velocity vector can be examined in relation with local movement of the flame front. The kinetic energy of turbulence in the burnt gas flow is increased in the frequency range that corresponds to the flamelet passing frequency. The kinetic energy of turbulence in the burnt gas flow is larger at low frequency but is smaller at high frequency than that in the approach flow. The turbulence intensity is significantly increased in the radial direction in the burnt gas flow, inducing anisot-rapy in an initially isotropic turbulence.